Air Flotation DAF

Dissolved air flotation (DAF) has been widely used over the last 40 yr for removal of oil and grease, suspended solids, and biochemical oxygen demand (BOD) from wastewater and other industrial process stream. The reliability and performance of DAF systems have been improved along with the increasing use of this technology, as shown in Table 7. 

The basic concept of DAF is to attach very small bubbles of air to emulsions in order to remove them from water. In this system, a side stream of oil is supersaturated under pressure with dissolved air so that air bubbles will carry the floatable particles vertically upward. A number of advanced DAF designs have contributed to the increased efficiency of this technology, for example  

Although DAF has been in use for 40 yr, the design criteria available to engineers are limited in design manuals. The major parameters of concern include hydraulic loading rate, solids loading rate, and air-to solids ratio. 

The hydraulic loading rate (HLR) is typically the primary design parameter for most industrial applications. The suggested value range from 11.73 to 234.70 m /m -min 

Dissolved Air Flotation Clarifiers-Brief History of Development 

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Dissolved Air Flotation. Dissolved air flotation (DAF) is used to separate suspended soflds and oil and grease from aqueous streams and to concentrate or thicken sludges. Air bubbles carry or float these materials to the surface where they can be removed. The air bubbles are formed by pressurizing either the influent wastewater or a portion of the effluent in the presence of air. When the pressurized stream enters the flotation tank which is at atmospheric pressure, the dissolved air comes out of solution as tiny, microscopic bubbles. Dissolved air flotation is used in many wastewater treatment systems, but in the United States it is perhaps best known with respect to hazardous waste because it is associated with the Hsted waste, K048, DAF flotation soflds from petroleum refining wastewaters. Of course, the process itself is not what is hazardous, but the materials it helps to remove from refining wastewaters. 

Low concentrations of oil can be removed by dissolved air flotation (DAF). In this process, an effluent recycle is pressurized in the presence of excess air, causing additional air to go into solution, in accordance with Henry s Law. When this water is discharged to the inlet chamber of the flotation unit at close to atmospheric pressure, the dissolved air comes out of solution in the form of tiny air bubbles which attach themselves to and become enmeshed in suspended solids and oil globules. The primary design criteria is the air/solids ratio, which is defined as the mass of air released divided by the mass of solids fed. Sufficient air must be released to capture the solids in the influent wastewater. The performance of DAF for the treatment of several... 

It should be noted that dissolved air flotation (DAF) is a more effective process for clarification.8-10 As shown in Appendix D, with an additional step of chromium reduction, the secondary treatment system effectively removed chromium (over 99%), copper (89%), cadmium (64%), lead (67%), and zinc (77%). 

API stands for the American Petroleum Institute and TEB stands for Thermal Emulsion Breaking. Figures 5.1 and 5.2 show two typical types of oil-water separators, gravimetric and parallel plate.7 A dissolved air flotation (DAF) clarifier is commonly used for polishing the effluent from an oil-water separator.8"1013... 

Dissolved air flotation (DAF) technology, requiring a short detention time (less than 15 min) and a small space, combined with its mobility, is technologically and economically feasible for treatment of washed wastewater or contaminated groundwater.57 58... 

Both dissolved air flotation (DAF) and electroflotation have been successfully applied to the removal of contaminants from surface water as well as groundwater.62 64... 

Perhaps the most efficient but least recognized process for groundwater decontamination is dissolved gas flotation, also known as dissolved air flotation (DAF), in which air is used for the generation of extremely line air bubbles having diameters less than 80 pm. 

A common modification of this process is dissolved air flotation (DAF), in which air under pressure is injected into the wastewater. DAF units are more efficient than conventional flotation clarifiers because more air is introduced into the wastewater, thereby removing more solids.43 5-59... 

A description is given of a unique solution for the problems of overloaded conventional activated sludge systems. A high-rate dissolved air flotation (DAF) clarifier is applied in series between the... 

Dissolved air flotation (DAF) is a process commonly used in refineries to enhance oil and suspended solids from gravity-separator effluent. In some refineries it is used as a secondary clarifier for activated sludge systems and as a sludge thickener. The process involves pressurizing the influent or recycled wastewater at 3-5 atm (40-70 psig) then releasing the pressure, which creates minute bubbles that float the suspended and oily particulates to the surface. The float solids are removed by a mechanical surface collector. 

Figure 14 Variations in dissolved air flotation (DAF) design. (A) Full-flow operation (B) split-flow operation (C) reeycle operation. (From Ref. 40.)...

Dissolved air flotation (DAF) is a commercially available, ex situ technology for the treatment of groundwater, process water, and wastewater contaminated with petroleum hydrocarbons. The... 

In this example, the development of a new flotation technique for waste water treatment is discussed. Dimensional analysis has been used since the onset of this work. It concerns the so-called Induced Air Flotation, IAF, which is an alternative to the well-known Dissolved Air Flotation, DAF, the latter being already discussed in Example 7. 

Dissolved air flotation (DAF) is a technique that uses minute air bubbles to enhance the flotation of oils and suspended materials not removable in reasonably sized gravity separators. The bubbles are formed by pressurizing aU or part of the waste flow and introducing air to a pressurization cell. Subsequent depressurization allows the bubbles to form, according to Henry s law. 

Continuous physicochemical PAC process systems involving the use of dissolved air flotation (DAF) clarifiers for clarification. 

PAC can be fed in the dry state using volumetric or gravimetric feeders or can be fed in slurry form. There are at least three major PAC producers, over 50 manufacturers of volumetric and gravimetric feeders, and over 50 manufacturers of slurry feeders (24-26). There are also many manufacturers of sequencing batch reactors (SBR) (22), dissolved air flotation (DAF) clarifiers (30), and centrifuges. 

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